Absolutely you can calibrate it out with a feedback system. However it you're not, my enlarger (EJC bulb in a DeVere) is nowhere near within 5%; it takes a good 300ms to warm up and nearly a second to cool down. Some of that will cancel, but there is a distinct difference in both density and grade. I'm using a microcontroller-based f/stop timer so I know that that's consistent within 10ms (half cycle AC); the problem is the thermal lag in the bulb.